A typical amplifier that amplifies, for example, an audio signal is a digital amplifier that uses a delta-sigma modulation. For example, PTL 1 discloses a digital switching amplifier that generates a quantization output signal by delta-sigma modulation of an audio input signal and that generates a switching signal by pulse amplification of the quantization output signal. The digital switching amplifier generates a feedback signal in a feedback loop for feedback on the switching signal by voltage reduction in the switching signal due to resistance division.
A structure disclosed in PTL 1 will be described with reference to FIG. 6(a). FIG. 6 illustrate the structure of digital amplifiers in conventional examples. FIG. 6(a) illustrates a digital amplifier 200, which is one of the conventional examples. As illustrated in FIG. 6(a), the digital amplifier 200 includes a delta-sigma modulator 201, a switching circuit 202, a power supply circuit 203, and an attenuator 241. The delta-sigma modulator 201 includes an integrator-adder group 211 and a quantizer 212. In the digital amplifier 200, an input signal that is an analog signal is inputted into a difference unit, and a feedback signal of a signal line S206 is inputted, as an input signal, into the difference unit by negative feedback from the switching circuit 202 via the attenuator 241. The difference unit calculates a difference between the input signal and the feedback signal and outputs a difference signal to a signal line S202.